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RIFLEX: a new rapid automated railhead inspection system

TWI has just completed a two-year to produce a system capable of non-destructively inspecting railheads and automatically logging defects at speeds up to 70mph. Acting as the consortium manager for RIFLEX, a European-funded project, TWI developed the inspection module for the mobile rail cart solution.

Inspection challenge

One of the main problems with current methods of inspecting railheads is the need for the sensing device to be in contact with the railhead itself, which inherently limits the speed of inspection. Current techniques – eddy current inspection, alternating current field measurement, conventional ultrasonic testing and magnetic flux leakage – have all proved inadequate for the envisaged resource-efficient rail transport system of the future, hampered by slow inspection speeds and limited defect detection.

For example, alternating current field measurement and the most widely used method, eddy current inspection, can only be applied at walking speed and are limited to detecting surface-breaking defects only. Ultrasonic testing is also a walking-speed technology, where the orientation of defects greatly affects the likelihood of detection, and is unable to detect surface defects. Magnetic flux leakage inspection does allow a faster inspection rate, up to 21mph, but it cannot detect defects below 4mm in size.

Fig. 1. EMAT multi-probe inspection configuration
Fig. 1. EMAT multi-probe inspection configuration

The RIFLEX project solution

The RIFLEX project developed a solution capable of delivering a major advancement in the non-destructive inspection of railheads within the European railway infrastructure. The solution enables faster inspection speed by using electromagnetic acoustic transducer (EMAT) technology. This technology avoids the need for contact with the railhead and the resulting prototype system (currently at technology readiness level six) is capable of inspecting rail at up to 70mph. Two EMAT probes are used for each rail, placed 200mm apart. This multi-probe solution enables sensitivity to flaws in all directions and increases the information recorded about the orientation and scale of any discontinuity, so that automated interpretation can be developed and enhanced.

The principle EMAT design was based on an industry standard which addresses the typical requirement for EMAT coils capable of generating Rayleigh waves. The design uses a single permanent magnet and a dual-layer racetrack coil. As well as developing the EMAT probes, TWI also developed the prototype system for both generating and receiving the EMAT signals. This system was based upon an enhanced acoustic pulser-receiver design capable of delivering higher levels of power into an RF coil as well as signal conditioning, digitising and data storage for up to four receiver EMATs.

The EMAT transmitting unit sends an acoustic wave across the surface of the rail, which is detected by the EMAT receiving unit. Any flaws in the surface or subsurface of the rail are detected as changes in these signals. The dual transducer mechanism is mounted on a rail running vehicle, so these signals are transmitted and received during transit. For this reason, rapid signal processing is required to capture the signals during motion. The proximity of the coils is controlled by a number of optical actuators which move independently to control the position of the coils relative to the surface of the rail. The coils are backed by permanent magnets which can be applied in various configurations to meet inspection requirements.

Backing up findings with testing

The RIFELX system as a whole is a novel, self-contained, non-contact railhead inspection system that can be integrated with existing inspection trains or attached to an inspection carriage system as deployed in the RIFLEX project.

The system has been fully trialled at Quinton Rail Technology Centre, UK. Hosted by RIFLEX project partner Rail Alliance, the facility provided the optimum indoor and outdoor locations for demonstrating the RIFLEX prototype. The next steps for the SME partners in the consortium are to increase the technology readiness level and move closer towards commercialisation.

Acknowledgement

The research leading to these results received funding from the European Union's Seventh Framework Programme managed by REA Research Executive Agency ( http://ec.europa.eu/rea/) (FP7/2007-2013) under grant agreement no 605115.


The RIFLEX project is a collaboration between TWI Ltd, NDT Consultants, D2S International, AIRTREN S.L., iKnowHow Informatics S.A., I-MOSS NV, University of Birmingham and Rail Alliance Ltd.

Contact us

For more information on the RIFLEX project visit  www.riflexproject.eu or email contactus@twi.co.uk.

A project video can be viewed at https://youtu.be/Vleu2SNJEWw.

Fig. 2. Trialling the RIFLEX system
Fig. 2. Trialling the RIFLEX system
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